A standard belt press as described in U.S. Pat. Nos. 4,417,866, 4,480,978, and 4,613,293 has a frame having horizontally extending and vertically spaced upper and lower plates defining a horizontally extending gap having an upstream end and a downstream end, vertically spaced upper and lower upstream drums rotatable about respective horizontal axes at the upstream end, vertically spaced upper and lower downstream drums rotatable about respective horizontal axes at the downstream end, and upper and lower endless belts spanned over the respective upper and lower drums and each having a working stretch lying between the plates and a return stretch. Upper and lower sets of rollers engaged between the working stretches and the respective plates can be recirculated as the belts are advanced to move the working stretches horizontally in a transport direction to displace a workpiece in the direction through the gap so that the working stretches are supported on the respective plates by these rollers. The entire press is also normally heated to activate a binder in the workpiece.
Typically the rollers have a diameter of between 15 mm and 25 mm, normally 20 mm, and are subjected to a pressure between 300N/cm.sup.2 and 600N/cm.sup.2 normally 500N/cm.sup.2. As a result the standard prior-art practice has been to use solid rods as the rollers. Such solid rods can be made to very tight tolerances of diameter, straightness, and the like. Nonetheless in a long press, which can exceed 50 m in length, this means that a huge mass of such rollers must be moved.
It has been suggested in German patent 3,534,996 filed Oct. 01, 1985 and in European patent 236,905 issued Apr. 03, 1991 and equivalent U.S. Pat. No. 4,807,525 to R. deBrock (based on DE 3,608,487 filed Mar. 14, 1986) to make the rollers tubular. These rollers are of extremely thin wall thickness, well under 2 mm, so that they deform in the press and act as spring elements. The service life of such rollers, which deform substantially in use, is therefore relatively short.